1. Field of the Invention
The present invention concerns a semiconductor device and a manufacturing method of the semiconductor device.
2. Description of Related Art
Along with scaling down of semiconductors in recent years, it has been demanded to increase the capacitor capacitance per unit area. One of methods for increasing the capacitor capacitance is to decrease the thickness of a capacitance dielectric film. However, even when the thickness of the capacitance dielectric film is decreased, the entire capacitor capacitance is not increased but sometimes decreased rather.
For example, Japanese Unexamined Patent Publication No. 2007-329496 describes that a thin silicon oxide film present between the upper portion of a lower electrode and a capacitance film comprising Ta2O5 acts as a parasitic capacitance to lower the entire dielectric constant thereby decreasing the capacitor capacitance upon forming the thin capacitance film. The technical means for solving such a problem is as described below. According to the patent document described above, after forming Ta2O5 over a TiN lower electrode, a heat treatment at 700 to 900° C. is performed to convert a portion of TiN into TiO2 at high dielectric constant. According to the method, (i) the capacitance film can be formed to a Ta2O5/TiO2 stacked structure at high dielectric constant. The heat treatment (ii) improves the film quality of Ta2O5. Further, since this adopts a structure of providing TiO2 of the capacitance film by way of a lower electrode comprising TiN over a polysilicon accumulation node, and (iii) even when the polysilicon accumulation node is oxidized, the silicon oxide film can be suppressed from acting as a parasitic capacitance. It is described that lowering of the capacitor capacitance upon decreasing the thickness of a capacitance film can be prevented due to (i) to (iii).
Further, Japanese Unexamined Patent Publication No. 2004-047633 describes a technique of forming a capacitance film over an Ru film (lower electrode) subjected to a preliminary heating treatment, thereby suppressing crackings in the capacitance film. That is, according to the patent document described above, crystal grains of the Ru film grow crystallographically into a stable state by the preliminary heat treatment. This suppresses further crystal growing of crystal grains of the Ru film upon heat treatment during formation of the capacitance film. It is described that crackings in the capacitance film due to crystal growing of the Ru film can be suppressed during formation of the capacitance film.
Further, Japanese Unexamined Patent Publication No. 2007-158222 describes that a capacitance film is formed over a lower electrode (TiN) in an amorphous state to make the capacitance film into an amorphous state thereby capable of decreasing the leak current of the capacitance film.
Further, Japanese Unexamined Patent Publication No. 2007-329286 describes that a semiconductor device satisfying higher capacitance and lower leak current simultaneously is provided by using an amorphous capacitance film (hafnium oxide film) with no addition of AlO. This patent document describes that a lower electrode of TiN is nitrided by remote plasma. The remote plasma processing intends to remove an oxide layer formed in the lower electrode forming step, thereby preventing lowering of the capacitor capacitance caused by the oxide layer of low dielectric coefficient that acts as a parasitic capacitance.